Multicast over SubT comms is not allowed

[tpet]

I am not able to bind to a multicast group.
E.g. the code below (excerpt from within a member function)

comms_client_ = std::make_shared<subt::CommsClient>("X1");
// subt::communication_broker::kMulticast == "multicast"
comms_client_->Bind(&SimpleRelay::comms_callback, this, subt::communication_broker::kMulticast, 20) // returns false

fails with
[ERROR 1599819990.746046087 /subt_ros_relay] OnBind address does not match origination. Attempted impersonation of a robot as robot[multicast].

I'm using an image based on osrf/subt-virtual-testbed:latest.

Is multicast supported for cave circuit? From the comms client docs it seems that it should be. ("kMulticast" doesn't work either.)

[AravindaDP]

@nkoenig @caguero Any updates on this? I also came across same issue and couldn't figure out how to properly use multicast functionality. Could there be a bug in underline CommsClient?

[peci1]

Solution proposed in #772.